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The trickiest part of the next phase may well be 802.11e, designed to allow quality-of-service protocols to run over Wi-Fi. Although video is often considered the stress test of a network, users wont often notice an error or two in a video stream, said Ian Sherlock, who manages wireless LAN product development for Texas Instruments. Users speaking in VOIP phones, on the other hand, quickly pick up on any network latency, which translates into unexpected pauses in the conversation.
The 802.11e upgrade will probably follow the example of the Wi-Fi security protocols, which have evolved through WEP through WPA and onto 802.11i.

Today, VOIP networks run on top of 802.11a, .11b or .11g, or in conjunction with some proprietary implementation of a Wi-Fi technology, Sherlock said.

In the first half of 2004, a substandard known as Wireless Multimedia Extensions (WME) will be rolled out, which uses a function called Enhanced Distributed Channel Access, Sherlock said, a simpler contention-based scheme. In simulated tests, TI found that a WME-based network could support about 50 handsets before a noticeable loss of data.
Currently, an 802.11e subgroup is defining Wireless Scheduled Multimedia, the second phase of 802.11e. If all goes as planned, WSM should roll out in the latter half of 2004, Sherlock said, using a more complex function called Hybrid Coordination Function Controlled Channel Access, or HCCA. HCCA allows the access point to initiate exchanges by "polling" the handsets every so often, and has proven less susceptible to data loss under load, Sherlock said. This protocol will probably support twice the number of handsets WME will, he said.
In all, VOIP networks will have to undergo at least two upgrades to take full advantage of 802.11e, Sherlock said. "With proper management, this will only require a software upgrade," he said, noting that equipment makers may opt to skip the first WME deployment and jump straight to WSM, which should begin to be designed into certified products by the third quarter of 2004.
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